TeamCity plug for Visual Studio 2010 is causing background build on loading solution

TeamCity plugin version ProductVersion=8.1.35.476&InstalledVsVersions=10.0;11.0
Server version:  TeamCity Enterprise 8.1.2 (build 29993)
Windows 7
VS 2010 10.0.40219.1 SP1Rel
plugin logging into TC server and Perforce.


Recently upgraded TC server and therefore TC plugin from v6.

Now when i load a solution in Visual Studio 2010, without invoking any other commands, i can see in procexp that the solution is being built: i.e. cl.exe/link.exe/other build steps are running.  VS doesn't show a build is in progress.  If i then start a build in VS, two builds are showing in procexp and the one build fails since files are locked by the other build.

any ideas?

thanks
terry